I am currently employed with a company that operate J31 and we carry out maintenance on our own aircraft and 3rd party work for other operators of the J31.
The aircraft are ok if you keep on top of them and work them, but if you do not use them regularly and have them sitting around they can start to be a pain. Parts are still fairly easy to get even though the aircraft has been around for a while. A lot of aircraft have been brought back into use recently that have been sitting in the desert for a few years so their popularity is on the up.
If you are looking at getting one get a good survey carried out it will be worth it in the long run. I have surveyed a few in the last few years and there are some dogs about. If the aircraft that you look at has been on the ground for a few years and does not meet all the requirements of TCAS II and TAWS these can be expensive modifications to carry out.
If you need any further details let me know.